The aims of the proposed investigations is to study the human immune response to group B streptococcal infections and to elucidate possible methods for the prevention of infant disease due to group B streptococci through immunoprophylaxis. The proposed studies will allow the immunochemical characterization of native capsular polysaccharides of each serotype strain, and the development of serologic assay to assess host response to infection by the development of serum type-specific antibody. It will also allow further information regarding reports that infant susceptibility to invasive infection with group B streptococci is significantly related to deficiency of type-specific maternal serum antibody. In addition, several laboratory methods to allow the rapid and early diagnosis of group B streptococcal infection in neonates are in progress. In addition, purified capsular polysaccharides from type III, group B Streptococcus have been tested in normal adults to assess safety and immunogenicity. Preliminary results indicate that the type III native capsular polysaccharide is immunogenic and safe in adults, and this may represent the first step in preventing infant disease through passive immunization via placental from women with vaccine-induced type-specific serum antibody. This antibody should remain in high concentrations from maternal transfer during that time when infants are susceptible to disease (the first 3 months of life).